The parent applications, which are incorporated herein in entirety by reference, relate to some of the ultrasonic system and method features herein disclosed.
Published background technology for the application of ultrasonic impact energy to the surface of polypropylene and thermoplastic materials for welding or riveting, is evidenced by U.S. Pat. No. 5,976,314 issued Nov. 2, 1999, by Manfred Sans for DEVICE FOR ULTRASONIC TREATMENT OF WORKPIECES. However, this teaching does not disclose a feasible system for the reworking of machined metal workpieces by ultrasonic impact machining methods wherein the machined metal surface and sub-surface thereunder is deformed to control surface texture and workpiece hardness, as does the present invention.
The application of ultrasonic energy to metal weld joints, as disclosed by S. E. Jacke in U.S. Pat. No. 3,274,033 issued Sep. 20, 1966 for ULTRASONICS, involves contacting an ultrasonically oscillating transducer horn directly upon a welded seam between abutting thin titanium alloy panels to process welding defects. However, this transducer horn system cannot deliver enough power to a massive metal workpiece body to effectively penetrate any considerable distance into sub-surface areas for deforming and compressing the surface and adjacent sub-surface regions and increasing the strength of massive metal bodies, such as cast iron used in various tool embodiments for compressive confrontation of mating surfaces.
Various specialty ultrasonic metal working impact tools, including hand operated transducers, are disclosed in the prior art for surface deformation and sub-surface plasticization of explicit shapes and contours, typically cylinders, rotating surface segments and planar sheets by direct mechanical interfacing of an ultrasonically vibrating head with a metallic surface work site. Typical disclosures are found in Russian Inventor's Certificates including: SU 1447646 A1, published Dec. 30, 1988; SU 1263510 A2, published Oct. 15, 1986; SU 1756125 A1, published Aug. 23, 1992; SU 1255405 A1, published Sep. 7, 1986; SU 1576283 A, published Jul. 7, 1990; SU 998104, published Jan. 5, 1981; SU 1214396 A, published Feb. 28, 1986; SU 1481044 A, published Sep. 28, 1987; and SU 1703417 A1, published Jan. 7, 1982 relating to direct mechanical contact between an oscillating ultrasonic transducer head oscillating at the prescribed ultrasonic frequency and the treated metallic object surface. These ultrasonic transducers in general dispose a single directly driven impact element coupled to a driving oscillator surface, which vibrates at a periodic ultrasonic frequency as applied to treatment of a welded structure to reduce welding defects.
French Patent No. 2,662,180 filed May 7, 1991 relates to a system for applying ultrasonically impulse energy for the special purpose of inducing plastic surface deformation at weld sites to correct welding defects in plastic materials. This prior art system, however, does not disclose satisfactory ultrasonic machining methods or systems or an ultrasonic transducer structure as afforded by the present invention or any structure or methods that could successfully develop and control ultrasonic energy intensity sufficient for general purpose ultrasonic impact machining by deforming both surface and sub-surface structure to a significant depth in a variety of working interface surface shapes of massive metallic bodies for compressively confronting mating surfaces.
Statnikov et al published documents IIW XIII-1617-96 and IIW XIII-1609-95 relate to the state of the art of hand held tools for applying ultrasonic impact energy directly from an oscillating transducer head at the impacting resonant frequency of the driving oscillator. These transducers are special purpose transducers with single impacting needles adapted to a system configuration for achieving the particular functional treatment of welded structure defects.
These prior art ultrasonic transducer systems have not provided satisfactory tools, systems or methods for reworking and machining metallic work interface surfaces of various shapes employed in frictional compressive and sliding contact, such as presented in rotary bearing surfaces, brake drums as well as sliding and reciprocating engine cylinders or wedges, propellers and the like, thereby to deform surface and sub-surface structure, hardness and texture for producing longer work life while bearing increased compressive work loads.
In general, the prior art ultrasonic transducer systems have not been able to provide high enough readily controlled impact power over work interfaces of considerable surface area on metallic workpiece interfacing surfaces to precisely control both the surface hardness and texture and the adjacent sub-surface structure at significant working depths exceeding normal wear tolerances. The prior art has produced ball peening and ultrasonic transducer impacting systems with enough power to reach the material's yield points for deformation treatment in the molten or plasticized state. However, this invention produces enough ultrasonic impact power to effectively reach the ultimate material strength of the body, and thus modify the surface layer.
Thus, such prior art systems and methods do not provide substantially universal ultrasonic transducer systems and methods suitable in size, power and control for achieving work functions, such as desirable for the repair or manufacturing of metallic work interfacing surfaces for compressive confrontation with mating surfaces. Nor is the prior art capable of plastically deforming and compressing surface and adjacent sub-surface regions to sufficient depths particularly for machining a variety of different surface configurations on massive metallic bodies thereby to attain specified end structure in both surface and sub-surface regions of a treated metallic workpiece. High power ultrasonic transducers also must be confined in size to machine internal cylindrical working surfaces of bearings, keyways and the like.
Also, the ultrasonic transducer must be of a nature to ultrasonically impact machine metallic objects of various interacting surface shapes to greater depths. For example, consider the problems of manufacturing and/or repairing a propeller having critical surface characteristics at blades, hubs and fillets of different shapes and masses, and being subject to various kinds of sub-surface defects, such as cavitation, corrosion, wear, cracks and welding stresses, which would deteriorate the reaction of marine propeller blade working surfaces in underwater compressive and sliding interface with saltwater. There has been no known successful multi-function system or method for ultrasonic impact machining of such diverse sets of conditions as incurred in the manufacture and in-service repairs of marine propellers.
The typical prior art manufacture and repair of marine propellers is expensive and complex and must employ a series of incompatible treatment methods, such as heat treatment of the metallic workpiece in a furnace, which cause defects which deteriorate the desired service as a marine propeller. Propellers are conventionally cast and left with sub-surface pores, cavities, cracks and geometric deviation from design shape. Manufacturing defects are detected by ultrasonic, X-ray, metric and other non-destructive tests. Conventional repairs are made by heat treatments and controlled cooling cycles, grinding, machining, welding depositions, and the like, which in turn introduce new stresses, fatigue and corrosive characteristics and are expensive and time consuming. In particular, the heat treatments are critical in the presence of transition surfaces, blade thickness variations, uneven mass distributions, etc. which tend to leave unevenly distributed thermal deformations and unfavorable residual tensile stresses that speed up corrosion, fatigue and wear failures in service, particularly in salt water environments.
It is also necessary to introduce various surface treatments after internal heat treatments, such as to supply protective coatings on propeller blades and the like, which in turn introduce surface imperfections that interfere with work surface operation. For example, required surface characteristics may range from in-service optical smoothness to specified degrees of surface roughness necessary to anchor an outer smoothing layer, and there has been no known prior art ultrasonic machining method or system for achieving this.
Thus, it is an object of this invention to ultrasonically machine workpiece working interface surfaces to achieve designated smoothness, hardness, surface deformation, surface relief, compressive stresses, friction, reflectivity and corrosion resistance and to remove surface and sub-surface defects.
It is a primary objective of the invention to employ ultrasonic impact surface and sub-surface plastic deformation tools, systems and methods for improving metallic workpiece surface strength while substantially reducing manufacturing procedures and costs.
Improvements of propeller reliability using ultrasonic impact machining is achieved by directing aperiodic force impulses on the workpiece surface with a freely axially moving impacting needle element driven from a primary ultrasonic energy delivery surface vibrating at the specified ultrasonic frequency.
It is critical in such operations to produce enough power for deforming surface and sub-surface regions of a workpiece to necessary depths. The present invention greatly increases output power by operation of a transducer driven from a periodic ultrasonic frequency energy source through a series of energy concentration stages operable at interfacing higher harmonic resonance frequencies operable at a Q-factor increase and significantly higher velocity imparted to needle-like freely axially moving impacting elements.